1. Field of the Invention
The present invention relates to a magnetron sputtering apparatus which may be used for depositing or forming a thin film on a wafer or each individual substrate thereon in order to fabricate semiconductor devices or electronic components, such as a magnetic disc, optical disc, or magnetic optical disc. It also relates to a method of depositing or forming a thin film on the wafer or each individual substrate thereon by making use of such a magnetron sputtering apparatus.
2. Description of the Prior Art
A typical magnetron sputtering apparatus that is known in the relevant prior art has been used widely, because of its simple construction, high productivity, and good reproducibility.
Specifically, a type of magnetron sputtering apparatus that is designed for fabricating semiconductor devices by a single wafer process has the following advantages:
(1) It can increase the rate at which a thin film or layer is deposited or formed on the wafer, and can minimize the effects of any gasesous impurities that may be produced during that process. This provides good quality thin films on the wafer; and
(2) It allows a thin film to be formed within the wafer or each individual substrate on the wafer in a controlled manner, and provides an identical profile, or geometrical configuration, for the thin film formed within every individual substrate or wafer.
FIGS. 14 and 15 show a typical prior art magnetron sputtering apparatus that has been used heretofore for the above particular purposes, which comprises a magnetron cathode including a circular target material 62, and a wafer 63 which contains individual substrates thereon. The substrates are placed with a specific spacing therebetween, with one facing opposite the other. The magnetron cathode also includes means 64 for producing a magnetic field, which means is placed behind the circular target material 62 and the wafer 63. This discharge provides the sputtering action upon the circular target material, so that a thin film can be formed or deposited on the wafer or each individual substrate thereon.
The magnetic field producing means 64 includes a center magnet 65 and an annular magnet 66 surrounding the outer circumferential edge of the center magnet 65, the other two magnets being connected by a yoke 67. The assembly 64 provides lines of magnetic force as shown by 68 which develop a magnetic field across the circular target 62. The circular target material undergoes the sputtering action which produces an annular erosion region 69 as shown by the dotted lines on the surface of the target 62. This annular erosion region 69 is caused by the rotation of the magnetic field producing assembly 64.
FIGS. 16 and 17 show another prior art magnetron sputtering apparatus which also has been used in past years. This apparatus is an improvement over the apparatus shown in FIGS. 14 and 15. In the apparatus shown in FIGS. 16 and 17, the magnetic field producing assembly 64 which is placed behind the circular target 62 has a construction that is different from that of the assembly 64 in the earlier described apparatus. Specifically, the magnetic field producing assembly 64 includes an annular magnet 66 which is disposed around the circumference of a yoke 67, and a central magnet 65 which is offset from the center axis of rotation 70 as shown in FIG. 17. On the side of the axis 70 opposite the side on which central magnet 65 is located, there are two auxiliary magnets 71 which are placed one on top of the other inside the annular magnet 66.
The prior art magnetron sputtering apparatus shown in FIGS. 16 and 17 has the following constructional features that distinguish it from the prior art apparatus shown in FIGS. 14 and 15. As shown in FIGS. 16 and 17, the central magnet 65, which is formed like a plate having a rectangular shape, is offset from the center axis of rotation 70 of the magnetic field producing assembly 64 to one side thereof, and the auxiliary plate magnets 71 (which are rubber sheets containing impregnated ferrite and which are placed one on top of another) are disposed inside the annular magnet 66. The number of auxiliary plate magnets 71, as well as the direction of the magnetic field developed by each of the sheets, may be changed. The erosion region (the portion of the target material that is eroded by sputtering) that appears on the surface of the circular target 62 consists of triple concentric circles 72a, 72b and 72c, as shown by the dotted lines in FIG. 16. This makes it possible to make more effective use of the target material, the utilization of which may amount to about 58%.
As described, the apparatus shown in FIGS. 16 and 17 provides an improvement over the apparatus shown in FIGS. 14 and 15, in that the target material can be utilized more effectively. Also, it can improve the step coverage of the surfaces of contact holes formed in, and the distribution of thin films formed on, the wafer or all individual substrates thereon, as compared with the apparatus in FIGS. 14 and 15. However, the problems of dust particles that may originate in the target material and may be transported across the spaces between the target and onto the wafer, eventually settling on the wafer or individual substrates thereon, remains unsolved.
It should also be noted that, in the use of the improved apparatus shown in FIGS. 16 and 17, the sputtering cannot take place from all the areas of the circular target material, with some areas of the target located around its center being subject to little or no sputtering action. It is noted that dust particles tend to settle on these areas, adhesively or not. The dust particles are thus easily transported from these areas toward the wafer or individual substrates thereon, during the sputtering process. When these dust particles settle on the thin films formed on some substrates on the wafer, they may affect the quality of those particular substrates, which may contain defects such as pin holes.
Another problem occurs with the contact holes formed in the wafer or each individual substrate thereon during the sputtering process. With the apparatus shown in FIGS. 16 and 17, it is difficult to provide a uniform thin film coating on all surfaces of the formed contact holes. The films on the contact holes, which are located at various points on the wafer, may become irregular. A further problem is the irregular thin film coating at each individual contact hole.